On 2015-07-04 15:01, Tom Van Baak wrote:
(the Japan earthquake in 2011 sped the earth up by 1.8 microseconds/day. The Sumatra quake on 26 Dec 2004 had a bigger effect: 6.8 microseconds)
Just in case you didn't know -- these are theoretical results only. There's a guy at JPL (Richard Gross) who does the calculations and any time there's a big seismic event he runs the simulations and out comes a number. That's pretty cool but the numbers so far are always smaller that what VLBI can actually measure. Still, it makes a nice press release and physics lesson. Buried in the articles is sometimes a clarification like "the researchers concluded the Sumatra earthquake caused a length of day change too small to detect, but it can be calculated". Some recent calculations: NASA Details Earthquake Effects on the Earth http://www.jpl.nasa.gov/news/news.php?release=2005-009 Chilean Quake May Have Shortened Earth Days http://www.jpl.nasa.gov/news/news.php?release=2010-071 Japan Quake May Have Shortened Earth Days, Moved Axis http://www.jpl.nasa.gov/news/news.php?release=2011-080 All Days Are Not Created Equal http://www.jpl.nasa.gov/news/news.php?feature=15 See also: http://geodesy.unr.edu/hanspeterplag/library/projects/tsunami_loading/RotGravSigSumatraEqv4_pre.pdf "While the modeled change in the Earth’s rotation that should have been caused by the 2004 Sumatran earthquake is less than the uncertainty in present-day measurements of the Earth’s rotation, it is still worth examining the measurements to see if an earthquake induced signal is present." http://www.obspm.fr/spip.php?page=imprimer&id_article=2193&lang=fr "the effect in the movement of the pole should be of a few centimetres in the polhodie and of a few microseconds of time in the duration of the day, which is not very likely to be detected seen the current precision of the observations." The Sumatran earthquake impact on Earth Rotation from satellite gravimetric measurements https://hal-insu.archives-ouvertes.fr/hal-00117348/document "For the length of the day Chao & Gross (2006) modeled the increment of axial inertia moment and obtained a drop of 2-6 µs confirmed by our result (5 µs). This effect is undetectable in the LOD, because the precision on this parameter is of 20 µs." This last paper is really interesting because it compares space-based models with terrestrial models. And all this is of interest to time nuts because the earth is an oscillator and events like this affect the phase, frequency, and ADEV of the planet.
Thanks for the good and interesting refs. One of the interesting points was that normal variations are multiples of those caused by earthquakes, and annual variations are up to 1ms and 1m. Another was that the jet streams produce large short term variations caused by temperature differences. Will this always turn up as an issue with all oscillators? ;^> -- Take care. Thanks, Brian Inglis _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
